Simulation of infills for seismic assessment of open ground storey RC frame buildings

Abstract

Un-reinforced masonry (URM) infilled RC framed buildings with open ground storey are the most common construction practice for modern multi-storey buildings in India. The complex infill-frame interaction under lateral loading makes the modeling and analysis of infilled frame difficult and the general design practice is to treat infills as non-structural elements and their stiffness, strength and interaction with frame is often ignored. The complex behavior of infilled frames gets further complicated when infills are placed irregularly in elevation keeping ground storey open for parking. Indian Standard, like many other national codes, does not provide any explicit guideline for modeling of infills and insight into the anticipated performance of the infilled frames. This paper takes a stock of modelling and controlling design provisions in some of the major national seismic design codes for URM infills and presents a macro model for URM infilled frames. Using the developed model, an analytical study is presented on effect of open ground storey on the seismic performance of RC frame buildings designed and detailed as per amendment of BIS (2002) requiring the beams and columns of the open ground storey to be designed for 2.5 times the design base shear for the corresponding uniformly infilled frame buildings.